We have shown that NO reacts with and deactivates dopamine (DA), norepinephrine (NE) and epinephrine (Epi). In addition, we have found that superoxide (O2-) as well as peroxynitrate (PN; ONOO-), the free radical product of the reaction of NO and O2-, can also deactivate catecholamines (CA), and are more potent that NO in this regard. Normally any O2-produced within the body is safely removed by naturally occurring superoxide dismutases (SOD). However, in situations where both NO and O2- are present in large quantities (such as inflammation or endotoxic shock) there is a preferential formation of PN. Endotoxic shock is characterized by severe hypotension, despite increased levels of endogenous CA, coupled with a loss of vascular responses (hyporeactivity) that develops to both exogenous and, presumably, endogenous CA. The clinical response to this problem, consisting of fluid resuscitation therapy coupled with intravenous (i.v) infusions of NE and DA, is limited as a result of this hyporeactivity. With this in mind, we believe that the finding that both O2- and PN diminish the bioreactivity of CA has major implications for understanding the development and, ultimately, the treatment of hypotension associated with endotoxic shock. Having already established the basis for our studies using the lipopolysaccharide (LPS) challenged model of endotoxic shock, we proposed to study this phenomenon further, using a conscious, unrestrained rat model of E. coli induced endotoxic shock. In addition, the interactions between NO and CA may have important implications for the modulation of sympathetic co-transmission under normal conditions. Using various experimental models of sympathetic neurotransmission we will examine to what extent the deactivation of CA by NO affects the co- transmission of neuropeptide Y (NPY) and adenosine triphosphate (ATP). Finally, we have confirmed that the reaction between O2- or PN and CA results in the formation of adrenochromes in endotoxic rats. Since these we have been reported to be cytotoxic we will examine the possibility that they contribute to the dysfunction that develops in endothelial and epithelial cells in endotoxic shock by exposing cultures of cells to adrenochromes and assaying for cellular damage and death. Adrenochromes may also interfere with sympathetic neurotransmission in their own right. In order to investigate this in more detail we plan to assay for the interference of adrenochromes with catecholamine uptake, and also examine whether these compounds affect sympathetic co-transmitter release.